Outline how the main pollutants are formed in vehicle engines and the environmental problems they cause. Explain why different types of vehicle engines produce different exhaust emissions

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Introduction

Skills for Chemistry: Open-book Paper 2007 Outline how the main pollutants are formed in vehicle engines and the environmental problems they cause. Explain why different types of vehicle engines produce different exhaust emissions. Nitrogen Oxide (NOx gasess) is formed when fuels are burnt. Traffic and cars are the biggest emitters of NOx in the United Kingdom. NOx is formed when air is heated above 800�C, where nitrogen and oxygen react. These temperatures are reached in lightening or in combustion processes. (i) At these high temperatures the oxygen will divide homolytically to make two separate radicals: O2 --> O + O Each radical then reacts in a catalytic cycle involving a nitrogen molecule and an oxygen molecule, which then forms nitrogen monoxide and oxygen radical: O + N2 --> NO + O N + O2 --> NO +O As the nitrogen monoxide cools it reacts with the oxygen to form nitrogen monoxide: 2NO + O2 --> 2NO2 NOx can also be formed when impure nitrogen compounds are burnt. (ii) A range of nitrogen oxides (NOx), such as nitrous oxide and nitrogen dioxide, which will form nitric acid or nitrous acid that will contribute to acid rain. ...read more.

Middle

Taken from http://uk.answers.yahoo.com/question/index?qid=20070318075942AAI0LoZ (ii) Taken from Article 2 (Page 7) Give a detailed account of the reaction of the reaction mechanisms involved in the production of acid rain from atmospheric nitrogen. NOx emissions cause an increase in environmental concern, as well as reacting with hydrocarbons because they are additionally oxidised in the atmosphere they contribute to the production of Acid rain. In addition, some of the emissions absorb infrared radiation from the sun and alter the balance between incoming radiation and outgoing radiation from the earth leading to climate changes world wide. The reaction mechanism * NO emissions in the lower atmosphere are eventually oxidised to NO2: 2NO + O2 --> 2NO2 NO + O3 --> NO2 --> O 2 * The NO2 can then react with OH radicals from water to form nitric acid (HNO3) which then falls to earth as acid rain: NO2 + OH --> HNO3 (i) Word count =119 words (i) Taken from Box 2; Article 1. Describe how heterogeneous catalysts are used to reduce levels of air pollution from vehicles. Your answer should include: An explanation of how heterogeneous catalysts work. ...read more.

Conclusion

2CO2 3. Oxidation of unburned hydrocarbons (HC) to carbon dioxide and water: 2CxHy + (2x+y/2) O2 ? 2xCO2 + yH2O These three reactions occur most efficiently when the catalytic converter receives exhaust from an engine running slightly above the stoichiometric point. (ii) Word count =320 (i) Taken from Article 2 (Page 8) (ii) Taken from http://en.wikipedia.org/wiki/Catalytic_converter#Three-way_catalytic_converters Identify the problems that scientists still need to solve in reducing harmful vehicle emissions. Currently around 75% of the U.K population lives within urban areas and poor air quality contributes substantially to ill health, there fore scientists need to find away to produce cleaner gases but even though the Noxer blocks are unable to remove all harmful fumes they are a 'step' forward to a more eco-friendly direction. (i) Also Scientists need to either find a chemical or use catalysts which have a reduced production of NOx as this would then have an overall impact on how many harmful gases are produced in the long run. (ii) Word count = 100 words Total word count = 1000 (i) Taken from Article 1 (Page 6) (ii) Take from Article 2 (Page 10) Sources Article 1 - Paved with titanium. Article 2 - Emission control. Website - http://uk.answers.yahoo.com/question/index?qid=20070318075942AAI0LoZ Website- http://en.wikipedia.org/wiki/Heterogeneous_catalysis Website - http://en.wikipedia.org/wiki/Catalytic_converter#Three-way_catalytic_converters Open-book Paper 2007 Rochester Grammar School Nawwal Dada Page Number 1 ...read more.

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